Actually, you probably
did fuck up the first meeting.
You're first message to her mentioned that you would fuck. It was super direct. I actually quite like it if your goal is to waste as little time as possible
Here's the thing: if she was willing to meet you after you told her you wanted sex;
then she turned up because she wanted sex.
Statistically, girls who meet up from dating websites are much more likely to have sex onthe first date. Take it from me that if you had already told her you wanted sex, then
she was absolutely, definitely, no questions asked interested in fucking you.
The reason she is now flaking, is because you didn't lead her to sex. You weren't aggressive enough in person. You're first message to her was direct and aggressive, but in person you weren't. It was incongruent, and hence the attractive guy in her mind that she was attracted to, didn't turn out to be the same guy she met in person. You didn't need to challenge her or neg her (you literally never need to neg a girl). You needed to lead her.
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Second note on text game -
DO NOT double text. you have one text to send her, then sit and wait until she texts back. I don't care if you wrote it wrong, if you changed you mind, if you're worried she took it the wrong way, whatever. Do Not text her twice in a row without her replying to your first text.
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My advice would be to leave it a few days and try and invite her for drinks in the late evening - say 9.30pm. This tends to spell sex in most girls minds. If she comes, then move things towards sex and physicallity. If she won't come, then move on and learn from the experience. It hurts, but to learn this stuff takes time

and you'll get there, so don't worry too much. Lots of hot girls in the world!
Good luck[/b]